This invention relates generally to gas turbine engines and more particularly to inlet guide vanes and shroud supports for such engines.
A turbofan gas turbine engine used for powering an aircraft in flight typically includes, in serial flow communication, a fan, a low pressure compressor or booster, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The combustor generates combustion gases that are channeled in succession to the high pressure turbine where they are expanded to drive the high pressure turbine, and then to the low pressure turbine where they are further expanded to drive the low pressure turbine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan and the booster via a second rotor shaft.
The high pressure compressor typically includes a series of stator vane stages used to compress air for engine and aircraft use. The first compressor stage adjacent to the booster is the inlet guide vane stage formed of a plurality of circumferentially arranged cantilevered inlet guide vanes. The inlet guide vanes may be actuated through a control system so as to optimize air flow for power and stall avoidance purposes. The guide vanes are retained between a stator case and an inner vane shroud. The stator case is coupled to the engine case. The space between the stator case and the shroud defines the volume of air passing through the high pressure compressor. The shroud provides an aerodynamic flowpath boundary of the high pressure compressor.
In some engines, the inlet guide vanes as well as other downstream stator vanes are variably actuated through the operation of one or more controllable vane actuators. An outer trunnion or spindle of the vane passes through the stator case and is coupled to a lever arm. The lever arm is coupled to an actuation ring that is connected to a vane actuator. One or more vane actuators effect movement to the series of circumferentially arranged stator vanes of each compressor stage. The vane is retained to the stator case through a combination of bushings, washers, and a lock nut that is threaded onto the outer trunnion.
The vane also includes an inner trunnion at its opposing end. That inner trunnion is used to retain the vane to the inner vane shroud. In most cases, a plurality of vanes spanned and retained by one shroud section. A plurality of shroud sections extends completely around the inner circumference of the compressor to retain all vanes. The inner trunnion of the vane is removably affixed to the shroud by way of a bushing. In addition, two shroud pins, one at each of the inner trunnions of the two end vanes of a particular shroud section, secure the shroud section to that set of vanes. For example, a shroud section made for five is secured to the inner trunnions of those five vanes by way of bushings. That is the only securing mechanism for the three interior vanes. The two outer vanes of the shroud section each has a modified inner trunnion or spindle with a hemispherical cut-out for accepting a retaining pin. The retaining pin passes transversely through the bushing and is designed to remain captured in the hemispherical cutout of the modified inner trunnion.
Groups of shroud sections are coupled together through a common shroud retainer or seal. The shroud retainer is designed to capture flanges or wings of the shroud sections below the inner trunnion. In those turbine engines where shroud retainers are employed, they are formed-to provide coverage to approximately one-quarter of the inner circumference of the compressor stage. That is, they extend approximately 90xc2x0 of the inner 360xc2x0 circumference, thereby capturing a plurality of shroud sections. Linking a series of vanes together using the shroud sections and then coupling a series of shroud sections together using the set of shroud retainers is intended tighten together the vanes. That along with the shroud pins is designed to reduce vane loosening, much like the spokes of a bicycle wheel are captured and retained together on a wheel hub.
Unfortunately, constant aerodynamic pressure forces associated with the operation of the high pressure compressor force movement of the inner shroud toward the stator case. The stress of that movement on the vane causes disparate movement between the inner trunnion of the pinned vanes and their associated shroud pins. The shroud pin provides very little retaining contact with respect to the vane trunnion. It therefore cannot bear the aerodynamic loads and friction from vane actuation and engine vibrations for the desired life expectancy of that portion of the compressor. Therefore, what is needed is a vane to shroud contact arrangement that will secure the vane to the shroud with reduced movement and resultant wear under expected engine operating conditions.
The above-mentioned need is met by the present invention, which provides a coupling assembly for retaining a rotatable structure to a fixed casing. The coupling or contact assembly includes a bushing designed to pass through the port of the segmented accurate inner shrouds and to retain the rotatable structure and a washer disposed within the port and positioned by way of a recessed hole in the shroud. A retainer removably coupleable to the inner shroud and disposed thereon captures the bushing between the inner shroud and the retainer. The assembly is suitable for use with turbofan engines having compressor stages. As previously indicated, the inlet guide vane stage of the compressor includes a plurality of variable guide vanes disposed between the stator casing and the inner vane shroud. The contact assembly of the present invention includes for each vane-to-shroud contact assembly a bushing removably retained within a port of the vane shroud for receiving the trunnion of the vane. The assembly also includes a washer positioned between a contact face of either the bushing or the inner shroud recessed hole shoulder and a trunnion button of the vane. Finally, a shroud sealing retainer removably coupleable to the outer surface of the shroud and disposed thereon captures the bushing between the washer and that retainer.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended l claims with reference to the accompanying drawings.